1. Field of the Invention
The present invention relates to a zoom optical system, and an image taking apparatus provided with such zoom optical system.
2. Description of the Related Art
There have been known various zoom optical systems including: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; and a third lens unit having a positive refractive power. In the optical system having such lens arrangement, since the first lens unit has a negative refractive power, the system is advantageous in reducing a diameter of the optical system while securing an appropriate angle of field in a wide-angle end. In addition, various four-unit types of zoom optical systems have also been known. As such zoom optical systems, there are known systems described in Japanese Patent Application Laid-Open Nos. 2004-318,099, 2004-318,106, and 2004-318,107.